Background: Stress is a prevalent health problem in modern society. If experienced for long periods of time it can lead to immune dysfunctions. Thus, public health management practices must include the assessment of stress. In health management settings, electrocardiography (ECG) is routinely used to assess cardiovascular health and make inferences about stress using information from heart rate variability (HRV). However, it is unclear whether stress assessment based on HRV can also be used to index immune function. Objectives: To compare stress that was determined by a measure of HRV (pNN50) from ECG with immune function indices (neutrophil, monocyte, and lymphocyte percentages) obtained from blood samples. Methods: A total of 184 healthy adults participated in the study, which took place in an examination room at the Health Management Center of The Affiliated Hospital of Hangzhou Normal University, China. Participants viewed a relaxing video while having a 2-min ECG recorded. They were then taken to have their blood drawn as part of their physical examination. Measures of stress (pNN50) were extracted from ECG, while measures of immune function (percentages of neutrophils, monocytes, and lymphocytes) were extracted from blood samples. Results: Stress correlated positively with neutrophil percentages (r = 0.21) and negatively with monocyte (r = –0.16) and lymphocyte percentages (r = –0.18). Conclusions: These findings show HRV analysis to be a potentially viable noninvasive and inexpensive method not only for indexing stress, but also predicting immune function, thus managing the health risks associated with stress.